Composite structures are used extensively in aircraft and other applications in which materials having a high strength-to-weight ratio are necessary. However, composite structures are costly since fabrication of such structures requires the layering of multiple materials. Depending on the particular application, a composite structure may be formed by layering individual sheets of material either manually or using an automated apparatus.
One type of composite structure which is commonly used as a support element in aircraft is the “I” beam or “T” stringer. These beam-type composite structures are generally formed by manually placing layers of composite material over a lay-up mandrel. An automated cutting machine cuts each layer of material, or prepreg, to the proper shape. The individual layers of the prepreg are then manually placed on separate lay-up mandrels. Once positioned, each layer of prepreg is manually conformed to the exterior contour of each lay-up mandrel to form two C-channels. Next, the C-channels and lay-up mandrels are rotated to facilitate joining of the C-channels to each other along their webs to form an I-beam. A radius filler is then placed in the triangular recesses formed in the center of the top and bottom flanges of the I-beam. Top and bottom composite reinforcement layers are then manually placed over the radius filler, which is then bagged and autoclave-cured.
The manual I-beam or stringer fabrication process is labor-intensive, time-consuming and attended by quality control issues. Therefore, automated methods of fabricating composite structures are being developed due to the drawbacks which are associated with manual fabrication of composite structures.